DNA methylation is a common epigenetic modification. Under the catalysis of DNA methyltransferase, the carbon atom at the 5th position of cytosine is methylated using the methyl group provided by S-adenosylmethionine, thereby transforming cytosine to 5-methylcytosine, which plays a vital role in the regulation of gene expression.
Cancer, also known as malignant tumor, is a disease caused by the abnormalities in the control of cell growth and proliferation mechanisms. Under normal circumstances, the growth and proliferation of cells are strictly regulated by some genes regulating the growth and development, including the oncogenes and the cancer suppressor genes, to maintain a normal physiological state; when affected by multiple factors such as radiation, chemical contamination, viral infection and endocrine imbalance, the activation of oncogenes and inactivation of tumor suppressor genes in vivo will be caused, thereby leading to the occurrence of cancer. In addition to the gene mutations, abnormal regulations of the epigenetics such as histone modification, DNA methylation also play an important role during the occurrence and development of tumor, the abnormalities of epigenetic modification can be found in a variety of cancers. In short, the occurrence of tumor is an extremely complex process, it is the result of abnormal regulation and its accumulation occurred in oncogenes, cancer suppressor genes and epigenetic modification in vivo.
DNA methylation has a close relation with the occurrence of cancer, the abnormalities of DNA methylation have been found in many cancers. DNA methylation has a certain degree of stability, it is an early event during the occurrence of cancer. In recent years, many studies have shown that abnormalities of DNA methylation can be used as a biomarker for cancer diagnosis. At present, abnormalities of DNA methylation in many specific gene promoter regions are used as a potential marker for the diagnosis for prostate cancer.
At present, the main diagnostic methods for prostate cancer are rectal diagnosis, serum PSA examination, and tissue immune biopsy, etc., in which the tissue immune biopsy is the gold diagnostic method for prostate cancer. However, since it is required to take the prostate tissue from a patient firstly, which will bring about great pains for the patient, it is not suitable for the previous diagnosis. PSA is currently used as a marker for the previous diagnosis for prostate cancer, but it is not quite accurate in terms of examination, and a certain gray zone exists. Therefore, it is very urgent to find a convenient and accurate diagnosis marker for the early diagnosis for prostate cancer.
Meanwhile, there are various methods for monitoring the DNA methylation in the prior art, for example, a quantitative analysis method for monitoring the DNA methylation disclosed in CN 104062334A, as another example, a DNA methylation chip technology. However, at the present stage, there exists a lack of a unified and more accurate criterion when determining whether the methylation is abnormal, therefore it is unable to predict the risk for cancer as early as possible through the change of the methylation level at specific sites.